It is quite common for in-dash automotive accessories, such as radios, CD players, and similar electronic components, to have detachable faceplates. Removing the faceplate when an automobile is unattended tends to discourage theft of the remaining components: removing the faceplate not only reduces the commercial value of the remaining components, but also reduces the likelihood that a potential thief will even notice the components.
Detachable faceplates require an effective electrical interface between the faceplate and the corresponding base module. Design goals for such an interface typically reflect a need for a small, reliable connector, utilizing as few signals as possible. Most designs also attempt to minimize electromagnetic interference.
In the past, this has not been a difficult design task since communications requirements between base modules and their corresponding faceplates have been modest. However, the increasing integration of computer functions into automobile accessories is likely to complicate the task of designing electrical interfaces between these components. Particularly, it is likely that removable faceplates will perform more complex functions than in the past, requiring sophisticated and high-speed data communications.
The inventors of the present invention were faced with just such a situation, in which a proposed faceplate would incorporate a color, pixel-addressable display panel having a size of 64.times.256 pixels. It was desired to enable a pixel refresh rate of at least 50 or 60 Hz, while minimizing electromagnetic emissions by avoiding high-frequency signals.
The conventional way of accomplishing the design objectives would have been to provide a parallel communications interface between the base module and the faceplate, so that pixel data could have been transferred in byte-size (or larger) words. This would have avoided the need for a high clock frequency, thereby reducing electromagnetic emissions.
Instead, however, the inventors devised a serial interface that allows refreshing of a 64.times.256 pixel display panel at a rate of up to 70 Hz. Despite such a high refresh rate, the serial interface transfers data at no more than 7.5 Mbits/sec. This transfer rate is low enough to avoid generation of any significant electromagnetic interference. Furthermore, the serial interface can be implemented with a minimum of signal lines so that a relatively inexpensive connector can be used.